Establish a cell-free system that will synthesize thionein (metallothionein) polypeptide chains from poly A-containing messenger RNA. This assay technique will provide a procedure to measure the amount of translatable mRNA for thionein that is present in liver and intestinal mucosa. These tissues will be derived from rats of varying zinc status developed either by changes in dietary zinc content or by parenteral zinc administration. The content of translatable thionein mRNA in the various subcellular fractions (polysomes and postribosomal supernatant) will be used to define the mechanism of zinc thionein synthesis and the role of this protein in zinc metabolism. Investigate the rate of degradation of zinc-thionein under a variety of dietary zinc intakes and to compare this rate to the degradation rate that had previously been calculated for zinc-thionein in rats fed adequate amounts of zinc. The susceptibility of zinc-thionein to degradation by lysosomal extracts will be investigated using purified zinc thionein and the demetalized apoprotein, thionein. Isolate and characterize the endogenous zinc chelator from intestinal cells and to investigate the specific role of this ligand in the absorption of zinc. Continue studies on the mechanism of zinc absorption with particular emphasis being placed on the kinetics of absorption, the carriers involved in the transport of zinc from the intestine to the systemic circulation. Both a vascularly perfused isolated intestine system and isolated intestinal epithelial cells will be used in this work.